1. Field of the Invention
The present invention relates to a sheet transport path switching mechanism suited to be applied to a sheet handling apparatus as represented by an image forming apparatus, such as copying machines, facsimile machines and various printers.
2. Description of the Related Art
An image forming apparatus, such as copying machines and facsimile machines, is known as one type of sheet handling apparatuses. The image forming apparatus is designed such that an optically read document image is formed on a photosensitive drum as an electrostatic latent image, and a toner image obtained by supplying toner to the electrostatic latent image is transferred (developed) onto a sheet. The developed sheet obtained through the toner transfer treatment is subjected to a fixing treatment using a fixing device, and then discharged outside through a given discharging transport path.
The discharging transport path is arranged to receive the sheet from a position directly below a development unit, which is disposed at an approximately middle position of the inner space of a housing of the image forming apparatus to extend horizontally, through the fixing device. For instance, as shown in FIG. 11, such a discharging transport path 100 includes a main transport path 101 extending approximately vertically upward, and a branch transport path 102 extending horizontally from a branch point 103 located at an appropriate position of the main transport path 101, toward a side sheet-discharge port 104 formed in the side surface of the housing of the image forming apparatus.
The main transport path 101 is arranged to allow its downstream end to be connected to an upper sheet-discharge port facing to a sheet-discharge tray (not shown) formed in the upper surface of the housing. A movable guide 110 is provided at the branch point 103 to allow the subsequent transportation for a sheet P transported from the development unit to be switched between the continuing transportation by the main transport path 101 and the branched transportation by the branch transport path 102.
The movable guide 110 comprises a shaft 111 extending to get across a transport path in a direction parallel to the width direction of the transport path, and a plurality of switching fins 112 fixed to the shaft 111 to extend in a direction orthogonal thereto. Each of the switching fins 112 has an approximately triangular shape in side view. More specifically, the switching fin 112 has a bottom edge formed in an arc shape concavedly curved obliquely downward, and a side edge located on the inward side of the housing and formed in an arc shape convexedly curved obliquely upward. The respective lower ends of the bottom and side edges intersect with one another to form an acuminate corner.
Both ends of the shaft 111 are pivotally supported by the inner surface of the housing corresponding to the branch point 103, to allow the movable guide 110 to be rotatably moved about the axis of the shaft 111. Specifically, the movable guide 110 can be rotationally moved in opposite directions to selectively take either one of a main posture where the side edges of the switching fins 101 retire to a position capable of avoiding the interference with the main transport path 106 and a branch posture where the bottom edges of the switching fins 101 face to the branch transport path 102 (FIG. 11 shows the movable guide 110 in the branch posture).
When the movable guide 110 is set up in the main posture, the sheet P fed from the fixing device to the main transport path 110 is guided by the right side-edges of the switching fins 112 in FIG. 11 to continuously pass through the main transport path 110, and then discharged from the upper sheet-discharge port to the sheet-discharge tray. Otherwise, when the movable guide 110 is set up in the branch posture, the sheet P passes through the branch transport path 102 while being guided by the bottom edges of the switching fins 112, and is then discharged outside from the side sheet-discharge port 104.
For example, the movable guide 110 is formed as a single piece through an injection molding process using a synthetic resin material to facilitate the reduction in material cost and production cost. In this case, the plurality (typically 10 to 20) of switching fins 112 become significantly deformable because they are integrated with the thin shaft 111 in a kite-train-like structure. Thus, if a relatively thick sheet P, such as a postcard, is fed to the branch point 103 where the movable guide 110 is arranged in the branch posture, it is difficult for the thick sheet P to turn around at a right angle while being guided and bent by the bottom edges of the switching fins 112. Consequently, the thick sheet P presses the bottom edges of the switching fins 112 upward to bend the shaft 111 convexedly upward. This precludes the sheet P from being properly fed toward the branch transport path 102, resulting in the occurrence of troubles, such as sheet jam.
While Japanese Patent Laid-Open Publication Nos. 11-130314 and 2000-211773 disclose a movable guide, none of the publications includes any description on the measure against the bending or deformation of the movable guide. Japanese Patent Laid-Open Publication No. 2001-316017 includes a description on one structure for preventing the deformation of a movable guide. Specifically, the Japanese Patent Laid-Open Publication No. 2001-316017 discloses a movable guide 110 having a metal reinforcing rod which is provided in the inside of a shaft 111 along the axis thereof to prevent the movable guide 110 from being deformed so as to avoid the occurrence of the aforementioned trouble.
However, the conventional movable guide 110 incorporating the metal reinforcing rod in the Japanese Patent Laid-Open Publication No. 2001-316017 involves problems of the increase in material cost due to the reinforcing rod, and the increase in production cost caused by the need for boring a through-hole over the entire longitudinal length of a produced movable guide along the axis of a shaft, and inserting the reinforcing rod into the through-hole.
Furthermore, in the above movable guide, the metal reinforcing rod is mixed with the synthetic resin body. Thus, when the movable guide is discarded, it is difficult to sort out the discarded components by materials. It is hard to say that the movable guide is desirable in view of waste treatment.